This invention relates to a voltage detection circuit for detecting a voltage boosted by an integrated high voltage generating system or the like.
As electronic appliances are becoming smaller in size recently, it becomes necessary to make the power supply voltage lower. However, in certain circuits incorporated into appliances, an operating voltage higher than the power supply voltage may be needed. In such a case, usually, an integrated high voltage generating system such as a charge pump is fabricated in a semiconductor integrated circuit, and the power voltage is boosted to a necessary operating voltage by this system. It is necessary, at this time, to detect the boosted voltage and to maintain the operating voltage within a predetermined range by the detection output.
For such purpose, conventionally, the boosted voltage has been detected by using a zener diode or a P-N junction of transistor.
When using a zener diode, however, since the zener diode must be formed in a semiconductor substrate, an extra mask and an extra inplanting process are needed. Therefore, the manufacturing process becomes complicated. Moreover, when the detection voltage is higher than about 5 V, the influence of the variation of the temperature become serious.
On the other hand, in case of using a P-N junction of transistor, since the breakdown voltage of P-N junction is used for detection, it is likely to cause the so-called "snake" phenomenon, that is, the electrons are trapped in the periphery of the P-N junction due to aging effect, and the voltage becomes higher than designed voltage as time passes. Therefore, it becomes difficult to detect the voltage accurately.